Nitrogen partitioning in orchard-grown Macadamia integrifolia

Fletcher, Andrew, Rennenberg, Heinz and Schmidt, Susanne (2010) Nitrogen partitioning in orchard-grown Macadamia integrifolia. Tree Physiology, 30 2: 244-256. doi:10.1093/treephys/tpp107

Author Fletcher, Andrew
Rennenberg, Heinz
Schmidt, Susanne
Title Nitrogen partitioning in orchard-grown Macadamia integrifolia
Formatted title
Nitrogen partitioning in orchard-grown Macadamia integrifolia
Journal name Tree Physiology   Check publisher's open access policy
ISSN 0829-318X
Publication date 2010-02-01
Year available 2009
Sub-type Article (original research)
DOI 10.1093/treephys/tpp107
Open Access Status Not Open Access
Volume 30
Issue 2
Start page 244
End page 256
Total pages 13
Editor Ram Oren
Place of publication Oxford, United Kingdom
Publisher Oxford University Press
Language eng
Subject C1
820206 Macadamias
060705 Plant Physiology
Formatted abstract
Nut yield is highly variable in commercial macadamia production, and to ensure that nitrogen (N) supply does not limit yield, high rates of N fertilizer are generally applied. To elucidate N source and sink relations in mature Macadamia integrifolia Maiden et Betche trees, we traced 15N label after injection into individual branches and, after soil application, analysed xylem sap and examined the effects of hedging on tree N relations. Xylem sap N and sugar composition and concentration changed in relation to phenology and tree management. Canopy position did not affect xylem sap N concentration but sampling date had a significant effect. Hedging in spring was associated with a rapid and dramatic reduction of the concentration of xylem sap N until the following autumn, but unhedged trees were not available to unequivocally assess the significance of the results. Following 15N-branch injection in winter, most 15N label was incorporated into flushing leaves and into bark. After 15N injection in spring, flushing leaves and flowers were most strongly 15N-labelled. In late spring, 15N label was equally incorporated by developing nuts that were retained or later abscised. Soil 15N application in summer resulted in 15N-labelling of outer and mid-canopy leaves. In the following spring, 15N label was translocated to flushing leaves, flowers and developing nuts. The results indicate that outer and mid-canopy leaves are the main N sink for soil-derived N during the vegetative phase and a N source for developing tissues during the reproductive phase. Our study provides evidence that N supply to developing nuts is not a primary cause for nut abscission, supporting the notion that high N fertilizer application rates do not improve nut retention. We propose that current orchard design and hedging practices should be reviewed in context of the role of outer canopy leaves as a source of N for reproductive tissues.
Keyword Amino acids
Nitrogen remobilization
Nilrogen storage
Nut retention
Xylem sap
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ
Additional Notes Available online December 11, 2009

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Created: Sun, 28 Feb 2010, 10:00:26 EST